Understanding of SQL standards

Why create SQL standards?

1. In order to make the products produced by database management software vendors well accepted by people. For example, the first vendor produces a database management software, which is the first SQL language to be used and accepted by people, another vendor also wants to produce its own database management software to sell money, so he must make the operations of his software easy to accept, and at this time it has been accepted by people, and, now there is no other language that is easier to operate than it, so another developer has to choose the first SQL language. Then, when many of them appear, there will be standards.

2. and ApplicationsProgramSoftware relationship. In the past, when developing applications, I wrote my own management data when writing applications.CodeHowever, as data increases, software requirements are getting higher and higher. It takes too much time to write data in an application separately, people have compiled an application for the data management function. Generally, few people operate this application separately. Most of these applications are part of the previous application, to apply the next software, the application developer must know the basic statements of the software. If the next software has its own independent language, the developer can't learn the language of optics, the interfaces provided by the next application are roughly the same.

The SQL standard is actually an operational standard, both select ...... From ...... The query operations are completed. However, the code inside the statement is very different.(For example, the size of a screw of a certain model is determined, that is, the so-called standard, but what material the screw is made of varies widely .)
Of course, generally, the birth of a new database management software is definitely a unique part of the family, or a part more powerful than other database management software, this part is not specified in the standard operation, so in order to enable people to apply more powerful functions in the operation, at the same time, it also meets the standards, some keywords have been added to previous standards. Of course, there are also other ways to change these keywords, so that standard SQL can be constantly updated.

Note: The SQL language is only the standard language of the relational database. The hierarchical database and the mesh database are not created based on the logical relationship between the two tables.